A hybrid vehicle driveline may include a driveline disconnect clutch. The driveline disconnect clutch allows a motor in the hybrid driveline to operate independently from an engine in the hybrid driveline. However, the motor may not always have capacity to supply torque that is sufficient to meet driver demand torque. Consequently, the engine may be started and coupled to the motor via the driveline disconnect clutch to meet the driver demand torque. Restarting the engine and coupling the engine to the motor may cause torque disturbances in the driveline that may be objectionable to the driver of the vehicle. Therefore, it may be desirable to provide a way to start the engine and provide the driver demand torque without creating driveline torque disturbances that may disturb the driver.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for operating a hybrid driveline, comprising in response to an increase in driver demand torque, supplying a portion of the increased driver demand torque before starting the engine; starting the engine; and supplying a remainder of the driver demand torque after starting the engine in response to speed of the engine being within a predetermined speed of a speed of a motor.
Supplying only a portion of driver demand torque before the engine is started allows motor torque to be held in reserve. By reserving a portion of available motor torque for starting an engine, it may be possible to reduce driveline disturbances when a driver demand torque increases to a level that may not be provided via the motor alone. The motor reserve torque may be output as a driveline disconnect is partially closed to rotate the engine for starting. In particular, the motor torque may be increased by an amount equivalent to an amount of torque transferred from the driveline to the engine so that the net driveline torque remains substantially constant (e.g., ±25 N-m) during engine restarting. Further, once the engine is started and the driveline disconnect clutch is being fully closed, motor torque output may be increased to smooth driveline torque as engine torque is delivered to the driveline.
The present description may provide several advantages. In particular, the approach may reduce driveline torque disturbances of a hybrid driveline. Further, the approach may improve vehicle drivability. Further still, the approach may reduce driveline wear, thereby increasing the operating life of the driveline.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.